Multi-rack, door-mounted heat exchanger

ABSTRACT

An air-cooling apparatus is provided which includes a securing mechanism for holding two or more separate electronics racks in fixed relation adjacent to each other, and a multi-rack door sized and configured to span the air inlet or air outlet sides of the racks. The securing mechanism holds the electronics racks in fixed relation with their air inlet sides facing a first direction, and air outlet sides facing a second direction. The door includes a door frame with an airflow opening. The airflow opening facilitates the ingress or egress of airflow through the electronics racks, and the door further includes an air-to-liquid heat exchanger supported by the door frame, and disposed so that air flowing through the airflow opening passes across the heat exchanger. In operation, the heat exchanger extracts heat from the air passing through the separate electronics racks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/115,404, filed May 25, 2011, and entitled “MULTI-RACK,DOOR-MOUNTED HEAT EXCHANGER”, which was published Nov. 29, 2012, as U.S.Patent Publication No. 2012-0300398 A1, and which is hereby incorporatedherein by reference in its entirety.

BACKGROUND

The power dissipation of integrated circuit chips, and the modulescontaining the chips, continues to increase in order to achieveincreases in processor performance. This trend poses a cooling challengeat both module and system levels. Increased airflow rates are needed toeffectively cool high-powered modules, and to limit the temperature ofthe air that is exhausted into the computer center.

In many large server applications, processors, along with theirassociated electronics (e.g., memory, disk drives, power supplies,etc.), are packaged in removable drawer configurations stacked within arack or frame. In other cases, the electronics may be in fixed locationswithin the rack or frame. Typically, the components are cooled by airmoving in parallel airflow paths, usually front-to-back, impelled by oneor more air-moving devices (e.g., fans or blowers). In some cases, itmay be possible to handle increased power dissipation within a singledrawer by providing greater airflow, through the use of a more powerfulair-moving device, or by increasing the rotational speed (i.e., RPMs) ofan existing air-moving device. However, this approach is becomingproblematic at the rack level in the context of a computer installation(i.e., data center).

The sensible heat load carried by the air exiting the rack is stressingthe capability of the room air-conditioning to effectively handle theload. This is especially true for large installations with “serverfarms”, or large banks of computer racks close together. In suchinstallations, liquid-cooling (e.g., water-cooling) is an attractivetechnology to manage the higher heat fluxes. The liquid absorbs the heatdissipated by the components/modules in an efficient manner. Typically,the heat is ultimately transferred from the liquid to an outsideenvironment, whether to air or other liquid.

BRIEF SUMMARY

The shortcomings of the prior art are overcome and additional advantagesare provided through the provision of an air-cooling apparatus forfacilitating cooling of airflow passing through multiple electronicsracks. The apparatus includes a securing mechanism for holding at leasttwo separate electronics racks in fixed relation adjacent to each other,and a multi-rack door sized and configured to span one of the air inletsides or the air outlet sides of the at least two separate electronicsracks held by the securing mechanism in fixed relation. The two separateelectronics racks are at least partially air-cooled, and each has an airinlet side and an air outlet side. The securing mechanism holds the atleast two separate electronics racks in fixed relation adjacent to eachother with the air inlet sides facing a first direction, and the airoutlet sides facing a second direction. The multi-rack door includes adoor frame with an airflow opening, and an air-to-liquid heat exchangersupported by the door frame. The airflow opening of the door framefacilitates the ingress and egress of external air through the two atleast separate electronics racks, and the air-to-liquid heat exchangeris disposed so that airflow through the airflow opening passes acrossthe air-to-liquid heat exchanger. The air-to-liquid heat exchangerextracts heat from the air passing thereacross, and air passing throughthe one of the air inlet sides or the air outlet sides of the at leasttwo separate electronics racks passes across the air-to-liquid heatexchanger. The securing mechanism includes an adapter frame sized andconfigured to mount to the at least two separate electronics racks atthe one of the air inlet sides or the air outlet sides thereof, and tohold the at least two separate electronics racks in fixed relationadjacent to each other. The adapter frame has a depth greater than adepth of the multi-rack door in a direction of airflow through the atleast two separate electronics racks from the air inlet sides to the airoutlet sides thereof.

In another aspect, a multi-rack assembly is provided which includes afirst electronics rack, a second electronics rack, and an air-coolingapparatus for extracting heat from airflow through the first electronicsrack and the second electronics rack. The first electronics rackincludes at least one heat-generating electronic component, and has anair inlet side and an air outlet side respectively enabling ingress andegress of external air through the first electronics rack. The secondelectronics rack includes at least one heat-generating electroniccomponent, and has an air inlet side and an air outlet side respectivelyenabling ingress and egress of external air through the secondelectronics rack. The air-cooling apparatus includes a securingmechanism for holding the first electronics rack and the secondelectronics rack in fixed relation adjacent to each other, and amulti-rack door sized and configured to span one of the air inlet sidesor the air outlet sides of the first and second electronics racks heldby the securing mechanism in fixed relation. The securing mechanismholds the first electronics rack and the second electronics rack infixed relation adjacent to each other, with the air inlet sides facing afirst direction and the air outlet sides facing a second direction. Themulti-rack door includes a door frame with an airflow opening, and anair-to-liquid heat exchanger supported by the door frame. The airflowopening of the door frame facilitates the ingress and egress of externalair through the first and second electronics racks, and theair-to-liquid heat exchanger is disposed so that airflow through theairflow opening passes across the air-to-liquid heat exchanger. Theair-to-liquid heat exchanger extracts heat from the airflow passingthereacross, and air passing through the one of the air inlet sides orthe air outlet sides of the first and second electronics racks passesacross the air-to-liquid heat exchanger. The securing mechanism includesan adapter frame sized and configured to mount to the first and secondelectronics racks at the one of the air inlet sides or the air outletsides thereof, and to hold the first and second electronics racks infixed relation adjacent to each other. The adapter frame has a depthgreater than a depth of the multi-rack door in a direction of airflowthrough the first and second electronics racks from the air inlet sidesto the air outlet sides thereof.

In a further aspect, a method is presented which includes: providing asecuring mechanism for holding at least two separate electronics racksin fixed relation adjacent to each other, the at least two separateelectronics racks being at least partially air-cooled, and each havingan air inlet side and an air outlet side, the securing mechanism holdingthe at least two separate electronics racks in fixed relation adjacentto each other with the air inlet sides facing a first a first directionand the air outlet sides facing a second direction; and providing amulti-rack door sized and configured to span one of the air inlet sidesor the air outlet sides of the at least two separate electronics racksheld by the securing mechanism in fixed relation, the multi-rack doorincluding: a door frame with an airflow opening, the airflow openingfacilitating the ingress and egress of airflow through the at least twoseparate electronics racks; and an air-to-liquid heat exchangersupported by the door frame and disposed so that airflow through theairflow opening passes across the air-to-liquid heat exchanger, theair-to-liquid heat exchanger extracting heat from the airflow passingthereacross, and wherein air passing through the one of the air inletsides or the air outlet sides of the at least two separate electronicsracks passes across the air-to-liquid heat exchanger; and wherein thesecuring mechanism includes an adapter frame sized and configured tomount to the at least two separate electronics racks at the one of theair inlet sides or the air outlet sides thereof, and to hold the atleast two separate electronics racks in fixed relation adjacent to eachother, and the adapter frame has a depth greater than a depth of themulti-rack door in a direction of airflow through the at least twoseparate electronics racks from the air inlet sides to the air outletsides thereof.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

One or more aspects of the present invention are particularly pointedout and distinctly claimed as examples in the claims at the conclusionof the specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 depicts one embodiment of a raised floor layout of a computerinstallation capable of being retrofitted with one or more air-coolingapparatuses, in accordance with one or more aspects of the presentinvention;

FIG. 2 is a top plan view of one embodiment of a single electronics rackwith an air-to-liquid heat exchanger mounted to an outlet door thereof,and with extracted heat being rejected to facility coolant via a coolantdistribution unit, in accordance with one or more aspects of the presentinvention;

FIG. 3 depicts one embodiment of a data center layout comprisingmultiple coolant distribution units providing liquid coolant to aplurality of air-to-liquid heat exchangers associated with a pluralityof electronics racks disposed in rows in the data center, and which isto be modified to include one or more air-cooling apparatuses, inaccordance with one or more aspects of the present invention;

FIG. 4 is a schematic of one embodiment of a coolant distribution unitwhich may be employed (in one embodiment) in association with anair-cooling apparatus, in accordance with one or more aspects of thepresent invention;

FIG. 5 is a partial cross-sectional elevational view of one embodimentof an electronic rack door with an air-to-liquid heat exchanger mountedthereto, taken along line 5-5 in FIG. 6, in accordance with one or moreaspects of the present invention;

FIG. 6 is a cross-sectional, top plan view of the door and air-to-liquidheat exchanger of FIG. 5, taken along line 6-6 in FIG. 5, in accordancewith one or more aspects of the present invention;

FIGS. 7A & 7B depict interior and exterior views, respectively, of oneembodiment of an electronics rack door having an air-to-liquid heatexchanger disposed therein, in accordance with one or more aspects ofthe present invention;

FIG. 8 is a partial isometric view of one embodiment of a singleelectronics rack, with an electronics rack door having an air-to-liquidheat exchanger, and illustrating coolant supply and return headers of adata center, in accordance with one or more aspects of the presentinvention;

FIG. 9 depicts a data center comprising two separate electronics racksdisposed adjacent to each other, each having a respective electronicsrack door with an air-to-liquid heat exchanger;

FIG. 10 depicts one embodiment of a multi-rack assembly comprising twoseparate electronics racks, held in fixed relation adjacent to eachother, and illustrating one embodiment of an air-cooling apparatus, inaccordance with one or more aspects of the present invention;

FIG. 11 is an exploded isometric view of one partial embodiment of themulti-rack assembly of FIG. 10, in accordance with one or more aspectsof the present invention;

FIG. 12A depicts assembly of a multi-rack assembly, such as depicted inFIGS. 10 & 11, and illustrating the securing mechanism of theair-cooling apparatus secured to one electronics rack of the at leasttwo separate electronics racks to be held in fixed relation, inaccordance with one or more aspects of the present invention;

FIG. 12B depicts the assembly of FIG. 12A, after hinged securement ofthe multi-rack door (with the multi-rack, door-mounted heat exchanger)to the adapter frame of the securing mechanism, in accordance with oneor more aspects of the present invention;

FIG. 12C depicts the assembly of FIG. 12B, and illustrates slidingengagement of a second electronics rack into fixed relation adjacent tothe first electronics rack employing the slidable engagement structuredisposed between the first electronics rack and the second electronicsrack, in accordance with one or more aspects of the present invention;

FIG. 12D depicts the multi-rack assembly of FIG. 12C, with the firstelectronics rack and second electronics rack shown held in fixedrelation adjacent to each other, and the adapter frame defining a commonairflow plenum directing air egressing from the first electronics rackand from the second electronics rack to pass through the multi-rack,door-mounted heat exchanger, in accordance with one or more aspects ofthe present invention;

FIG. 12E depicts a variation on the multi-rack assembly of FIG. 12D,wherein adjustable ducting structures are provided within the multi-rackdoor to accommodate a smaller-sized, air-to-liquid heat exchanger withinthe door, while ensuring that substantially all air passing through theair outlet sides of the two separate electronics racks passes across thesmaller-sized, air-to-liquid heat exchanger, in accordance with one ormore aspects of the present invention;

FIG. 13A depicts an alternate embodiment of a multi-rack assemblycomprising an air-cooling apparatus which includes an adapter frameholding at least two separate electronics racks disposed in fixedrelation to each other, a filler frame which assists in defining acommon airflow plenum at the air outlet sides of the racks of differentdepths, and a multi-rack, door-mounted heat exchanger, in accordancewith one or more aspects of the present invention;

FIG. 13B depicts an alternate embodiment of the multi-rack assembly ofFIG. 13A, wherein a smaller-sized, air-to-liquid heat exchanger isemployed within the multi-rack door, in accordance with one or moreaspects of the present invention; and

FIG. 14 depicts an alternate embodiment of the multi-rack assembly ofFIGS. 10-12E, wherein the adapter frame holding the at least twoseparate electronics racks in fixed relation adjacent to each other hasa depth greater than a depth of the multi-rack door in a direction ofairflow through the two racks, thereby defining a larger, common airflowplenum between (in this example) the air outlet sides of the electronicsracks and the multi-rack, door-mounted heat exchanger, in accordancewith one or more aspects of the present invention.

DETAILED DESCRIPTION

As used herein, the terms “electronics rack”, “rack-mounted electronicequipment”, and “rack unit” are used interchangeably, and unlessotherwise specified include any housing, frame, rack, compartment, bladeserver system, etc., having one or more heat generating components of acomputer system or electronics system, and may be, for example, a standalone computer processor having high, mid or low end processingcapability. In one embodiment, an electronics rack may comprise aportion of an electronic system, a single electronic system, or multipleelectronic systems, for example, in one or more sub-housings, blades,books, drawers, nodes, compartments, etc., having one or moreheat-generating electronic components disposed therein. An electronicsystem(s) within an electronics rack may be movable or fixed relative tothe electronics rack, with the rack-mounted electronic drawers of amulti-drawer rack unit and blades of a blade center system being twoexamples of systems (or subsystems) of an electronics rack to be cooled.

“Electronic component” refers to any heat generating electroniccomponent of, for example, a computer system or other electronics unitrequiring cooling. By way of example, an electronic component maycomprise one or more integrated circuit dies and/or other electronicdevices to be cooled, including one or more processor dies, memory diesand memory support dies. As a further example, the electronic componentmay comprise one or more bare dies or one or more packaged dies disposedon a common carrier.

As used herein, “air-to-liquid heat exchanger” means any heat exchangemechanism characterized as described herein through which liquid coolantcan circulate; and includes, one or more discrete air-to-liquid heatexchangers coupled either in series or in parallel. An air-to-liquidheat exchanger may comprise, for example, one or more coolant flowpaths, formed of thermally conductive tubings (such as copper or othertubing) in thermal or mechanical contact with a plurality of air-cooledcooling fins. Size, configuration and construction of the air-to-liquidheat exchanger can vary without departing from the scope of theinvention disclosed herein. A “liquid-to-liquid heat exchanger” maycomprise, for example, two or more coolant flow paths, formed ofthermally conductive tubings (such as copper or other tubing) in thermalor mechanical contact with each other to facilitate conduction of heattherebetween. Size, configuration and construction of theliquid-to-liquid heat exchanger can vary without departing from thescope of the invention disclosed herein. Further, as used herein, “datacenter” refers to a computer installation containing one or moreelectronics racks to be cooled. As a specific example, a data center mayinclude one or more rows of rack-mounted computing units, such as serverunits.

One example of facility coolant and system coolant is water. However,the concepts disclosed herein are readily adapted to use with othertypes of coolant on the facility side and/or on the system side. Forexample, one or more of the coolants may comprise a brine, afluorocarbon liquid, a liquid metal, or other similar coolant, orrefrigerant, while still maintaining the advantages and unique featuresof the present invention.

Reference is made below to the drawings (which are not drawn to scale tofacilitate understanding of the invention), wherein the same referencenumbers used throughout different figures designate the same or similarcomponents.

As shown in FIG. 1, in a raised floor layout of an air cooled computerinstallation or data center 100 typical in the prior art, multipleelectronics racks 110 are disposed in one or more rows. A computerinstallation such as depicted in FIG. 1 may house several hundred, oreven several thousand microprocessors. In the arrangement of FIG. 1,chilled air enters the computer room via floor vents from a supply airplenum 145 defined between a raised floor 140 and a base or sub-floor165 of the room. Cooled air is taken in through louvered covers at airinlet sides 120 of the electronics racks and expelled through the back(i.e., air outlet sides 130) of the electronics racks. Each electronicsrack 110 may have one or more air-moving devices (e.g., fans or blowers)to provide forced inlet-to-outlet airflow to cool the electroniccomponents within the rack. Supply air plenum 145 provides conditionedand cooled air to the air-inlet sides of the electronics racks viaperforated floor tiles 160 disposed in a “cold” air aisle of the datacenter. The conditioned and cooled air is supplied to plenum 145 by oneor more air-conditioning units 150, also disposed within data center100. Room air is taken into each air-conditioning unit 150 near an upperportion thereof. This room air comprises in part exhausted air from the“hot” air aisles of the data center defined by opposing air outlet sides130 of the electronics racks 110.

Due to the ever increasing airflow requirements through the electronicsracks, and limits of air distribution within the typical computer roominstallation, recirculation problems within the room may occur. Thisrecirculation can occur because the conditioned air supplied through thefloor tiles may only be a fraction of the airflow rate forced throughthe electronics racks by the air moving devices disposed within theracks. This can be due, for example, to limitations on the tile sizes(or diffuser flow rates). The remaining fraction of the supply of inletside air may be made up by ambient room air through recirculation, forexample, from an air outlet side of a rack unit to an air inlet side.This recirculating flow is often very complex in nature, and can lead tosignificantly higher rack inlet temperatures than might be expected.

The recirculation of hot exhaust air from the hot aisle of the computerroom installation to the cold aisle can be detrimental to theperformance and reliability of the computer system(s) or electronicsystem(s) within the racks. Data center equipment is typically designedto operate with rack air inlet temperatures in the 15-32° C. range. Fora raised floor layout such as depicted in FIG. 1, however, temperaturescan range from 15-20° C. at the lower portion of the rack, close to thecool air floor vents, to as much as 32-42° C. at the upper portion ofthe electronics rack, where hot air can form a self-sustainingrecirculation loop. Since the allowable rack heat load is limited by therack inlet air temperature at the “hot” part, this temperaturedistribution correlates to an inefficient utilization of available airconditioning capability. Computer installation equipment almost alwaysrepresents a high capital investment to the customer. Thus, it is ofsignificant importance, from a product reliability and performance viewpoint, and from a customer satisfaction and business perspective, toachieve a substantially uniform temperature across the air inlet side ofthe rack unit.

FIG. 2 depicts one embodiment of a cooled electronic system, generallydenoted 200. In this embodiment, electronic system 200 includes anelectronics rack 210 having an inlet door 220 and an outlet door 230,which have openings to allow for the ingress and egress of external air,respectively, through the air inlet side and air outlet side ofelectronics rack 210. The system further includes at least oneair-moving device 212 for moving external air across at least oneelectronic system or component 214 positioned within the electronicsrack. Disposed within outlet door 230 is an air-to-liquid heat exchanger240 across which the inlet-to-outlet airflow through the electronicsrack passes. A coolant distribution unit 250 is used to buffer theair-to-liquid heat exchanger from facility coolant in a facility coolantloop. Air-to-liquid heat exchanger 240 removes heat from the exhaustedinlet-to-outlet airflow through the electronics rack via circulatingsystem coolant, for rejection in coolant distribution unit 250 tofacility coolant in a facility coolant loop 260, that is, via aliquid-to-liquid heat exchanger 252 disposed therein. This coolingapparatus advantageously reduces heat load on existing air-conditioningunits within the data center, and facilitates cooling of electronicsracks by cooling the air egressing from the electronics rack and thuscooling any air recirculating to the air inlet side thereof.

As shown in FIG. 2, a system coolant loop 245 couples air-to-liquid heatexchanger 240 to coolant distribution unit 250. In one embodiment, thesystem coolant employed is water. By way of example, such a system isdescribed in U.S. Pat. No. 7,385,810 B2, issued Jun. 10, 2008, andentitled “Apparatus and Method for Facilitating Cooling of anElectronics Rack Employing a Heat Exchange Assembly Mounted to an OutletDoor Cover of the Electronics Rack”.

In one implementation, the inlet and outlet plenums of the air-to-liquidheat exchanger mount within the door and are coupled to coolant supplyand return manifolds disposed beneath a raised floor. Alternatively,system coolant supply and return manifolds or headers for theair-to-liquid heat exchangers may be mounted overhead the electronicsracks within the data center. In such an embodiment, system coolantenters and exits the respective coolant inlet and outlet plenums at thetop of the rack door, using flexible coolant supply and return hoses,which are at least partially looped and are sized to facilitate openingand closing of the rack door (containing the air-to-liquid heatexchanger). Additionally, structures may be provided at the ends of thehoses to relive stress at the hose ends, which results from opening orclosing of the door.

FIG. 3 is a plan view of one embodiment of a data center, generallydenoted 300, employing cooled electronics systems. Data center 300includes a plurality of rows of electronics racks 210, each of whichincludes an inlet door 220 at the air inlet side, and a hinged outletdoor 230 at the air outlet side, such as described above in connectionwith the embodiment of FIG. 2. In this embodiment, each outlet door 230supports an air-to-liquid heat exchanger and system coolant inlet andoutlet plenums. Multiple coolant conditioning units 250, referred tohereinbelow as pumping units, are disposed within the data center (alongwith one or more air-conditioning units (not shown)). As shown, in oneembodiment, each pumping unit forms a system coolant distributionsubsystem with one row of a plurality of electronics racks. Each pumpingunit includes a liquid-to-liquid heat exchanger where heat istransferred from a system coolant loop to a facility coolant loop.Chilled facility coolant, such as water, is received via facilitycoolant supply line 301, and is returned via facility coolant returnline 302. System coolant, such as water, is provided via a systemcoolant supply header 310 extending over the respective row ofelectronics racks, and is returned via a system coolant return header320 also extending over the respective row of electronics racks. In oneembodiment, the system coolant supply and return headers 310, 320 arehard-plumbed within the data center, and preconfigured to align over andinclude branch lines extending towards electronics racks in a respectiverow of electronics racks.

FIG. 4 depicts one embodiment of a coolant distribution unit 250 for(for example) a data center such as depicted in FIG. 3. Liquid-to-liquidheat exchanger 252 cools system coolant passing through the systemcoolant loop (comprising system coolant supply header 310 and systemcoolant return header 320). In one embodiment, the system coolant hasundergone heating (and possibly partial vaporization) within therespective air-to-liquid heat exchangers disposed within the outletdoors of the electronics racks. The facility coolant loop coupled toliquid-to-liquid heat exchanger 252 comprises facility coolant supplyline 301 and facility coolant return line 302, which in one embodiment,provide chilled facility water to the liquid-to-liquid heat exchanger. Acontrol valve 401 may be employed in facility coolant supply line 301 tocontrol facility coolant flow rate through the liquid-to-liquid heatexchanger 252. After the system coolant cools within liquid-to-liquidheat exchanger 252, the coolant is collected in a reservoir 410 forpumping via a redundant pump assembly 420 back to the respective row ofelectronics racks via system coolant supply header 310. As shown in FIG.4, a bypass line 430 with a bypass valve 431 may be employed to controlthe amount of system coolant fed back through the system coolant supplyheader, and hence, control temperature of system coolant delivered tothe respective air-to-liquid heat exchangers mounted to the doors of theelectronics racks.

FIGS. 5 & 6 depict one embodiment of outlet door 230 supportingair-to-liquid heat exchanger 240, and system coolant inlet and outletplenums 501, 601. Referring to both figures collectively, outlet doorframe 231 supports a rigid flap 500, which attaches, for example, bybrazing or soldering, to a plate 610 secured between the system coolantinlet plenum 501 and system coolant outlet plenum 601.

In FIG. 5, right angle bend 510 is shown disposed at the top of systemcoolant inlet plenum 501. This right angle bend defines a horizontalinlet plenum portion, which extends above the top of door 230. Thecoolant inlet to system coolant inlet plenum 501 is coupled to a connectcoupling 511 for facilitating connection thereof to the respectivesupply hose, as described above. In this embodiment, the air-to-liquidheat exchanger comprises a plurality of horizontally-oriented heatexchange tube sections 520. These heat exchange tube sections 520 eachcomprise a coolant channel having an inlet and an outlet, with eachcoolant channel being coupled to the system coolant inlet plenum 501 andeach coolant channel outlet being coupled to the system coolant outletplenum 601. A plurality of fins 530 are attached tohorizontally-oriented heat exchange tube sections 520 for facilitatingtransfer of heat from air passing across the air-to-liquid heatexchanger to coolant flowing through the plurality of heat exchange tubesections 520. In one embodiment, the plurality of fins arevertically-oriented, rectangular fins attached to horizontally-orientedheat exchange tube sections 520.

By way of specific example, FIGS. 7A & 7B depict one embodiment of anelectronics rack door 700 with a cooling apparatus mounted thereto,which as explained below, may be configured and sized as a multi-rackdoor and heat exchanger, in accordance with one or more aspects of thepresent invention. This cooling apparatus includes an air-to-liquid heatexchanger 715 across which exhausting air from the air outlet side ofthe electronics rack(s) (not shown) flows. As illustrated, air-to-liquidheat exchanger 715 is disposed within an airflow opening in a door frame710 which vertically mounts along a first edge 711 to the electronicsrack(s) (or as explained below, an adapter frame holding multiple racksin fixed relation). The cooling apparatus includes a system coolantinlet plenum 720 and system coolant outlet plenum 725 which (in thisembodiment) extend vertically into and along a second edge 712 of heatexchanger door 700. As illustrated, second edge 712 of heat exchangerdoor 700 is in opposing relation to first edge 711, which hingedlymounts to one or more electronics racks or adapter frames. Thus, in thisembodiment, the system coolant inlet and outlet plenums 720, 725 aredisposed remote from the edge of the heat exchanger door mounted to theelectronics rack(s). This will advantageously reduce stress (in anoverhead supply and return implementation) on the system coolant supplyand return hoses, during opening or closing of the door, particularlywhen the first ends of the supply and return hoses are affixed inparallel relation on top of the rack door to extend towards the firstedge of the rack door. As illustrated, system coolant inlet plenum 720includes a coolant inlet 721 which has a connect coupling 722 forfacilitating fluid tight connection to the system coolant supply hose(not shown). Similarly, system coolant outlet plenum 725 includes acoolant outlet 726 with a connect coupling 727 to facilitate fluid tightconnection to a system coolant return hose. In one embodiment, theseconnect couplings are quick connect couplings such as the commerciallyavailable quick connect couplings offered by Colder Products Company, ofSt. Paul, Minn., U.S.A., or Parker Hannifin, of Cleveland, Ohio, U.S.A.

FIGS. 7A & 7B also illustrate one embodiment of a stress reliefstructure 730 attached to an upper surface 713 of door 700. Stressrelief structure 730 includes a first opening 731 and a second opening732 which are respectively configured to receive the system coolantsupply hose and the system coolant return hose.

FIG. 8 depicts one embodiment of electronics rack 210 comprising ahinged outlet door 700 with an air-to-liquid heat exchanger 715 disposedtherein, and illustrating overhead system coolant supply and returnheaders 800, 801, respectively. As shown, system coolant supply andreturn hoses 810, 811 couple the air-to-liquid heat exchanger 715 influid communication with the system coolant supply and return headers800, 801, respectively. In one embodiment, system coolant supply andreturn hoses 810, 811 are sufficiently sized to allow for translationaland rotational movement of the hoses with opening or closing of the heatexchanger door 700. If desired, retention loops could be provided forconstraining movement of the hoses at multiple locations on top of theelectronics rack.

Those skilled in the art will note that the door, door frame andair-to-liquid heat exchanger embodiments depicted in FIGS. 2-8 arepresented by way of example only. For example, a multi-rack door with amulti-rack, door-mounted heat exchanger, such as described hereinbelow,may be implemented with similar cooling structures such as thosedescribed above in connection with FIGS. 2-8, or in various alternateembodiments thereof. For instance, in one alternate embodiment, thesystem coolant supply and return manifolds could be disposed beneath theelectronics racks in a raised floor data center. Further, the particulardesign of the air-to-liquid heat exchanger can vary without departingfrom the one or more aspects of the present invention disclosed herein.

FIG. 9 illustrates a generalized depiction of two adjacent electronicsracks 910 disposed, for example, within a row of electronics rackswithin a data center. As in the above-described embodiments, eachelectronics rack 910 includes one or more air-moving devices 912 formoving air from an air inlet side 901 to an air outlet side 902 andacross, for example, one or more electronic components (or systems)disposed within electronics rack 910 to be air-cooled. Heated airflow911 egresses through the air outlet side of electronics rack 910 andinto an outlet door 920 comprising an air-to-liquid heat exchanger 930.As described above, air-to-liquid heat exchanger 930 extracts heat from(in this example) the airflow 911 egressing from the air outlet side 902of electronics rack 910. Although this cooling approach works well, andis in use in many data centers today, further enhancements in heatremoval, energy efficiency and reduced hardware costs of the heatremoval system are desired.

Thus, disclosed hereinbelow with reference to FIGS. 10-14 are variousenhanced multi-rack assemblies (with multi-rack doors and multi-rack,door-mounted heat exchangers), in accordance with one or more aspects ofthe present invention. As explained below, the air-cooling apparatusesdisclosed herein allow standard depth IT rack units to be assembled sothat a single, door-mounted heat exchanger spans multiple racks forsimultaneously cooling air ingressing into or egressing from themultiple electronics racks. More particularly, the apparatus disclosedherein enables two or more racks, including industry-standardelectronics racks, to be mechanically coupled (or assembled) and cooledusing a single, multi-rack door comprising a multi-rack, door-mountedheat exchanger. This multi-rack assembly improves energy efficiency andreduces costs of the heat exchange system in achieving heat removal from(for example) industry-standard IT racks. Advantageously, the apparatusdisclosed herein can be retrofitted onto existing electronics rackswithin existing data centers, with little or no modification to theracks themselves. The apparatus disclosed herein can be applied to avariety of electronics racks, including industry-standard frames, andcan even be applied to two or more frames of different widths and/ordifferent depths. In addition, a lower airflow impedance is obtained bythe air-cooling apparatus disclosed, compared with, for example, theabove-described door-mounted air-to-liquid heat exchangers, which arededicated to cooling airflow through a single electronics rack. This inturn enables improved performance, and greater robustness of the ITequipment cooling system. Advantageously, the multi-rack doors andmulti-rack, door-mounted heat exchangers disclosed herein require fewerhoses and connections for supply and return of system coolant, and thusrequire less volume of coolant to be employed within the data center toachieve a given amount of heat removal. In addition, the air-coolingapparatuses disclosed achieve a higher increase in coolant temperatureacross the heat exchanger, thereby enabling more efficient heat transferto the external environment, and allow an opportunity for a higher inletcoolant temperature, which can enable a chiller capacity reduction.

In accordance with aspects of the present invention, improvements incapacity for heat removal, energy efficiency and cost savings areaccomplished by providing a multi-rack, door-mounted heat exchangerwhich provides, in one embodiment, a single air-to-liquid heat exchangerwhich spans the air inlet sides or the air outlet sides of multipleadjacent electronics racks. The multi-rack heat exchanger disclosedherein provides a higher percentage of effective heat exchanger surfacearea in opposing relation to the surface areas of the air inlet sides orthe air outlet sides of two or more adjacent electronics racks beingheld in fixed relation adjacent to each other. In comparison to themulti-rack heat exchanger disclosed herein, dedicated door-mounted heatexchangers, such as depicted in FIG. 9, provide a smaller heat exchangersurface area, and the individual rack doors require substantial areawhich cannot be used for heat removal or for the airflow path due, forexample, to space requirements for coil returns and the mechanicalblockages inherent in the door frame. Cost improvements are achieved dueto similar material and fabrication efficiencies of the air-coolingapparatus disclosed. Additionally, cost benefits are achieved by, forexample, an at least approximately 50% reduction in the coolant deliveryand return structures, including the door-mounted coolant inlet andoutlet manifolds, and the coolant supply and return hoses.

FIG. 10 depicts one embodiment of a multi-rack assembly, in accordancewith one or more aspects of the present invention. As shown, themulti-rack assembly includes a multi-rack door 1020 mounted to (in thisembodiment) two separate electronics racks 1010, which are held in fixedrelation to each other via a securing mechanism 1000. The two separateelectronics racks 1010 each comprise one or more air-moving devices 1012(such as fans or blowers) for providing an external airflow 1011 throughthe electronics racks from air inlet sides 1008 to air outlet sides 1009of the electronics racks. In one implementation, a door frame 1021 ofmulti-rack door 1020 includes an airflow opening 1019 which facilitatesegress of the airflow 1011 passing through the two separate electronicsracks 1010. Note that electronics racks 1010 are separate, stand-aloneelectronics racks, and may be one of a variety of conventionallyavailable IT racks comprising one or more heat-generating electroniccomponents (or systems) to be cooled. For example, standard, 24-inchwide IT racks, with a 40-inch depth, can be employed in the multi-rackassembly disclosed. Such racks can accommodate all depths of standard ITequipment, and can be installed through the typical door accessavailable in today's data center. The apparatus disclosed hereinprovides a method to combine, for example, two or more standard IT rackstogether (after they are transported to the data center) for cooling,using a single, multi-rack, door-mounted heat exchanger. Further,although illustrated with respect to a two-rack assembly, theair-cooling apparatuses disclosed herein could be adapted to mount tothree or more separate electronics racks employing, for example, anappropriately-configured securing mechanism and multi-rack door.

In the rack assembly embodiment of FIG. 10, the securing mechanism 1000comprises an adapter frame 1025 mounted to air outlet sides 1009 ofelectronics racks 1010. As explained further below, adapter frame 1025can be configured as a solid-walled flange or structural extender having(for example) a rectangular-shaped cross-section in a directiontransverse to the direction of airflow through the electronics rack. Inone implementation, structural extender 1025 forms an airtight seal,with the two separate electronics racks 1010 along upper, lower and sideedges thereof at either the air inlet sides or the air outlet sides,with the air outlet side rack assembly being illustrated in FIG. 10 byway of example only. The frame adapter 1025 and multi-rack door 1020together are configured to form a common airflow plenum 1031 between theair outlet sides 1009, door frame 1021, and air-to-liquid heat exchanger1030 mounted within door frame 1021 of multi-rack door 1020. Adjustableducting structures 1023 are provided within door frame 1021 tofacilitate defining the common airflow plenum and ensuring thatsubstantially all airflow passing through electronics racks 1010 passesacross air-to-liquid heat exchanger 1030. As explained further below,adjustable ducting structures 1023 may comprise one or more expandableor telescoping ducting plates, which are configured and positioned todirect airflow 1011 to pass across air-to-liquid heat exchanger 1030.The air-to-liquid heat exchanger 1030 is supported by door frame 1021and disposed so that air flowing through the airflow opening 1019 passesacross air-to-liquid heat exchanger 1030. In operation, theair-to-liquid heat exchanger extracts heat from the air passingthereacross.

In the embodiment illustrated, multi-rack door 1020 is hingedly 1022mounted along a vertical edge thereof to adapter frame 1025 of thesecuring mechanism 1000. As shown, securing mechanism 1000 furtherincludes one or more slidable engagement structures 1040 disposed, forexample, between the two or more separate electronics racks 1010 tofacilitate holding the two separate electronics racks in fixed relationadjacent to each other. Slidable engagement structure 1040 allows, forexample, a first electronics rack to be slidably positioned alongsideand to be held adjacent to a second electronics rack for assembly into amulti-rack assembly using the air-cooling apparatus disclosed herein, asexplained further below.

FIG. 11 illustrates an exploded view of a partial embodiment ofmulti-rack assembly, in accordance with one or more aspects of thepresent invention. As illustrated, two separate electronics racks 1010are positioned adjacent to each other and are held in fixed relation toeach other via an adapter frame 1025 configured to mount to (e.g.,encircle) the edges of the two (or more) adjacent electronics racksalong upper, lower and side edges thereof. Multi-rack door 1030 is sizedand configured to mount to adapter frame 1025. Adapter frame 1025provides, in one aspect, a mechanical structure for holding the two ormore electronics racks together. Further, adapter frame 1025 forms asingle vertical plane for the multi-rack door to mount to, andaccommodates (in one embodiment) a hinge assembly and latching assemblywhich allow the multi-rack door to be latched closed or rotated open foraccess to, for example, the air inlet sides or the air outlet sides ofthe two or more adjacent electronics racks held in fixed relationadjacent to each other by the adapter frame. Rotating open themulti-rack door facilitates inspection or servicing of the electronicsracks, or more particularly, the IT systems located within the two ormore adjacently-held electronics racks.

In addition to an adapter frame 1025, the securing mechanism of themulti-rack assembly disclosed herein may include, in one embodiment, oneor more mechanical devices to hold the opposite sides of the electronicsracks from the adapter frame together to achieve the multi-rackassembly. These mechanical devices may include: nuts/bolts (where holesare available and appropriately placed in both electronics racks);clamps (where holes are unavailable); or cable loops with tighteningmechanisms (which encompass, for example, the front sides or back sidesof both racks), etc.

In an alternate embodiment, the multi-rack door 1020 and multi-rack,door-mounted heat exchanger 1030 may be mounted directly to, forexample, the air outlet sides of the two or more adjacent electronicsracks, with alternative securing mechanisms being provided than theadapter frame 1025 illustrated in FIGS. 10 & 11. In such embodiments,the electronics racks themselves could be configured to receive themulti-rack door via, for example, hinged mounting of the door directlyto one of the electronics racks. Although not shown, the multi-rack door1020 includes coolant inlet and outlet manifolds and hose attachments,as described above with respect to the door-mounted heat exchangersdepicted in FIGS. 2-8. As noted above, the coolant may comprise avariety of types of coolant such as water or a refrigerant, selected tooptimally extract heat from air passing through the two or more separateelectronics racks held in fixed relation to each other by the securingmechanism of the apparatus. Further, the coolant supply and return hosesmay couple the coolant inlet and outlet manifolds within the multi-rackdoor to coolant supply and return headers disposed above the electronicsracks, or coolant supply and return plenums disposed, for example, in asupply air plenum below a raised floor supporting the electronics racks.

FIGS. 12A-12D depicts further details of the air-cooling apparatus andmulti-rack assembly disclosed herein. In FIG. 12A, an assembly is shownwherein adapter frame 1025 is affixed to, for example, the air outletside 1009 of a first electronics rack 1010, and slidable engagementstructure 1040 has been mounted to one side of electronics rack 1010. Inaddition, the multi-rack door 1020 is shown being attached to adapterframe 1025 via hinged mounting assemblies 1022. Multi-rack door 1020includes a door frame 1021 having an airflow opening 1019. Within doorframe 1021, an air-to-liquid heat exchanger 1030 is supported anddisposed so that air flowing through airflow opening 1019 passes acrossair-to-liquid heat exchanger 1030, with air-to-liquid heat exchanger1030 extracting heat from the air passing thereacross. Air-to-liquidheat exchanger 1030 and airflow opening 1019 are sized and configured sothat substantially all air passing through the air inlet sides or theair outlet sides of the two or more separate electronics racks 1010passes across the air-to-liquid heat exchanger 1030. In one embodiment,adjustable ducting structure 1023 within multi-rack door 1020facilitates directing airflow across air-to-liquid heat exchanger 1030.As noted above, coolant inlet and outlet manifolds and coolant supplyand return hoses coupled to the manifolds are also associated withmulti-rack door 1020. Further, multi-rack door 1020 includes, in oneembodiment, a sealing gasket to seal the door to adapter frame 1025, anda latch mechanism 1200 for latching the multi-rack door to adapter frame1025.

In FIG. 12B, the multi-rack door has been hingedly 1022 mounted toadapter frame 1025, and in FIG. 12C, a second electronics rack 1010 isshown being slid into position alongside the first electronics rack1010, having the slidable engagement structure 1040 mounted to the sidethereof. In one embodiment, slidable engagement structure 1040 maycomprise a T-shaped structure, with flanges extending over the topsurfaces of the electronics racks 1010 to facilitate securing of theslidable engagement structure to the respective electronics racks. Thoseskilled in the art will note that other configurations of the slidableengagement structure may also be employed for positioning and holdingthe adjacent electronics racks in fixed relation to each other.

In FIG. 12D, the two separate electronics racks 1010 are shown disposedin fixed relation, and held in position by the adapter frame 1025 andslidable engagement structure 1040, as well as possibly other mechanicalsecuring devices (such as described above) mounted, for example, to theair inlet and/or the air outlet sides of electronics racks 1010.Electronics racks 1010 include one or more air-moving devices 1012,which establish airflow 1011 through electronics racks 1010 that isexhausted out through multi-rack door 1020, and in particular, acrossair-to-liquid heat exchanger 1030 through airflow opening 1019. Asexplained above, air-to-liquid heat exchanger 1030 extracts heat fromthe airflow 1011 passing thereacross. Multi-rack door 1020 and adapterframe 1025 define a common airflow plenum 1031 between air outlet sides1009 of electronics racks 1010 and air-to-liquid heat exchanger 1030.Adjustable ducting structures 1023 within multi-rack door 1020facilitate defining this common airflow plenum 1031 and ensure thatsubstantially all airflow 1011 passing through electronics racks 1010passes across air-to-liquid heat exchanger 1030. As illustrated,air-to-liquid heat exchanger 1030 and structures 1023 are sized suchthat substantially all air passing through airflow opening 1019 passesacross air-to-liquid heat exchanger 1030.

In the alternate multi-rack assembly of FIG. 12E, the two or moreseparate electronics racks held in fixed relation adjacent to each otherare assumed to produce less heat than in the example of FIGS. 12A-12D.In such a case, a smaller air-to-liquid heat exchanger 1210 may bemounted within door frame 1021 of multi-rack door 1020. In thisembodiment, the airflow opening 1019 in door frame 1021 is substantiallythe same as in the multi-rack door 1020 of FIGS. 12A-12D. However,adjustable ducting structures 1023 are expanded or telescoped toaccommodate the smaller air-to-liquid heat exchanger 1210 disposedwithin door frame 1021. The adjustable ducting is expanded to ensurethat substantially all air passing through the electronics racks 1010passes across the smaller air-to-liquid heat exchanger 1210. Other thanbeing smaller (e.g., to accommodate a smaller heat load), air-to-liquidheat exchanger 1210 is similar to air-to-liquid heat exchanger 1030described above and may be, in one embodiment, an air-to-liquid heatexchanger such as depicted and described above in connection with FIGS.2-8. Note also that adjustable ducting structures 1023 may compriseslidable wall structures which may be expanded or retracted dependingupon the size of the air-to-liquid heat exchanger mounted within thedoor frame. Thus, the air-to-liquid heat exchanger may be selectivelysized for the heat load of the particular electronics racks held infixed relation within the multi-rack assembly. Advantageously, the samemulti-rack door may thus be used with different air-to-liquid heatexchangers.

This concept is also illustrated in FIGS. 13A & 13B, wherein in FIG.13A, a larger air-to-liquid heat exchanger 1030 is shown disposed withindoor frame 1021 of multi-rack door 1020, and in FIG. 13B, a smallerversion of the air-to-liquid heat exchanger 1210 is shown disposedwithin door frame 1021 of multi-rack door 1020, with adjustable ductingstructures 1023 being appropriately configured or adjusted to ensurethat substantially all airflow through the two or more separateelectronics racks passes through the air-to-liquid heat exchanger.

In the embodiments of FIGS. 13A & 13B, a first electronics rack 1300 isshown to be of less depth than a second electronics rack 1010. In thiscase, the electronics racks may have the same heat load, or differentheat loads. As illustrated, a filler structure (or flange) 1310 isconfigured and sized to extend the depth of first electronics rack 1300to substantially equal the depth of the second electronics rack 1010.This filler structure comprises, in one embodiment, a rectangular-shapedwall structure which has solid upper, lower and side walls, thatessentially extend the common airflow plenum 1031 to air outlet side1309 of first electronics rack 1300 being held in fixed relationadjacent to second electronics rack 1010. Filler structure 1310 alsofacilitates establishing a co-planar edge for adapter frame 1025 tomount to, notwithstanding the differently-sized electronics racks.

In FIG. 14, an adapter frame 1400 is shown having a larger depth tocreate a larger common airflow plenum 1031 between the air outlet sides1009 of the adjacently-held electronics racks 1010 and air-to-liquidheat exchanger 1210. One or more air-moving devices 1012 facilitateairflow through the adjacently-held electronics rack 1010, with airexhausting from the air outlet sides 1009 into the common airflow plenum1031, passing across air-to-liquid heat exchanger 1210 and existingthrough airflow opening 1019 in door frame 1021 of multi-rack door 1020.In this embodiment, multi-rack door 1020 hingedly 1022 mounts along onevertical edge to adapter frame 1400, and latches 1200 at an oppositeedge to adapter frame 1400. In one embodiment, adapter frame 1400 has alarger depth than a depth of the multi-rack door 1020 in a direction ofairflow through the two separate electronics racks 1010.

Advantageously, disclosed herein is a cooling apparatus which includes amulti-rack door that attaches to two or more slidably engagedelectronics racks housing one or more heat-generating electronic systemsor components with the same or variable heat load. The multi-rack doorincorporates an air-to-liquid heat exchanger for cooling the heat loadof the electronics racks to which the multi-rack door is attached,either at the air inlet side or the air outlet side of the racks. Asecuring mechanism is provided which holds the electronics racks infixed relation to each other, with the air inlet sides facing a firstdirection and the air outlet sides facing a second direction. Thesecuring mechanism includes an adapter frame to which the multi-rackdoor hingedly mounts. The adapter frame may be employed with a fillerstructure to allow the multi-rack door to mount to differently-sizedelectronics racks, which helps to optimize airflow and heat removal fromthe multi-rack assembly. For example, where two shallow-depth heatexchangers are to be secured for cooling using a multi-rack door, theadapter frame (and optionally, the filler structure) facilitatesco-planarity of the resulting rack assembly with other racks in the datacenter, thereby helping the resultant aisle configuration to begeometrically aligned at the data center level. Further, internaladaptable structures, such as adjustable ducting structures, areprovided to accommodate different-sized heat exchangers within themulti-rack door. These adjustable structures preferentially position theair-to-liquid heat exchanger within the door frame, and facilitatedefining a common airflow plenum to direct the airflow across theair-to-liquid heat exchanger.

Those skilled in the art will note from the above description that themulti-rack, door-mounted heat exchanger of the air-cooling apparatusdisclosed herein has (in one embodiment) a larger surface area than thesurface areas of the individual air inlet sides or air outlet sides ofthe electronics racks held in opposing relation therewith. Themulti-rack door and air-to-liquid heat exchanger disclosed hereinadvantageously provide a high-heat capacity heat removal, ahigh-efficiency heat removal, a lower cost, and support standard ITelectronics racks. The air-cooling apparatus disclosed can be readilyretrofitted to two or more electronics racks within a data center, andthe air-to-liquid heat exchanger size can be tailored to optimize heatremoval for the multi-rack assembly. Differently-sized air-to-liquidheat exchangers may be employed within the multi-rack door toeffectively tailor the cooling required dependent on the heat load ofthe two or more separate electronics racks being cooled. The result is amore efficient coolant distribution to the areas of the data centerwhere the heat transfer occurs, with more width in the door beingdevoted to heat transfer than compared with dedicated air-to-liquid heatexchangers per electronics racks, as described above. This also resultsin a lower pressure drop through the air-to-liquid heat exchanger due toless restriction to airflow, meaning (in one embodiment) thatlower-speed air-moving devices may be employed within the electronicsracks. Using the adjustable ducting structures disclosed herein, thedifferently-dimensioned air-to-liquid heat exchangers may be separatelyaccommodated within the multi-rack doors (thus enabling cooling to betailored to the particular electronics racks). In addition, theair-cooling apparatus disclosed herein can be disassembled from theelectronics racks when desired, for example, for reconfiguration of thedata center.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” (andany form of comprise, such as “comprises” and “comprising”), “have” (andany form of have, such as “has” and “having”), “include” (and any formof include, such as “includes” and “including”), and “contain” (and anyform contain, such as “contains” and “containing”) are open-endedlinking verbs. As a result, a method or device that “comprises”, “has”,“includes” or “contains” one or more steps or elements possesses thoseone or more steps or elements, but is not limited to possessing onlythose one or more steps or elements. Likewise, a step of a method or anelement of a device that “comprises”, “has”, “includes” or “contains”one or more features possesses those one or more features, but is notlimited to possessing only those one or more features. Furthermore, adevice or structure that is configured in a certain way is configured inat least that way, but may also be configured in ways that are notlisted.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below, if any, areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The embodiment was chosen and described in order to explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention throughvarious embodiments and the various modifications thereto which aredependent on the particular use contemplated.

What is claimed is:
 1. An air-cooling apparatus comprising: a securingmechanism for holding at least two separate electronics racks in fixedrelation adjacent to each other, the at least two separate electronicsracks being at least partially air-cooled and each having an air inletside and an air outlet side, the securing mechanism holding the at leasttwo separate electronics racks in fixed relation adjacent to each otherwith the air inlet sides facing a first direction and the air outletsides facing a second direction; and a multi-rack door sized andconfigured to span one of the air inlet sides or the air outlet sides ofthe at least two separate electronics racks held by the securingmechanism in fixed relation, the multi-rack door comprising: a doorframe with an airflow opening, the airflow opening facilitating theingress or egress of airflow through the at least two separateelectronics racks; an air-to-liquid heat exchanger supported by the doorframe and disposed so that airflow through the airflow opening passesacross the air-to-liquid heat exchanger, the air-to-liquid heatexchanger extracting heat from the airflow passing thereacross, andwherein air passing through the one of the air inlet sides or the airoutlet sides of the at least two separate electronics racks passesacross the air-to-liquid heat exchanger; and wherein the securingmechanism comprises an adapter frame sized and configured to mount tothe at least two separate electronics racks at the one of the air inletsides or the outlet sides thereof, and to hold the at least two separateelectronics racks in fixed relation adjacent to each other, and theadapter frame has a depth greater than a depth of the multi-rack door ina direction of airflow through the at least two separate electronicsracks from the air inlet sides to the air outlet sides thereof.
 2. Theair-cooling apparatus of claim 1, wherein the multi-rack door ishingedly mounted to the adapter frame.
 3. The air-cooling apparatus ofclaim 2, wherein the adapter frame comprises a structural extenderconfigured to mount to the at least two separate electronics racks atthe one of the air inlet sides or the air outlet sides thereof, and todefine a common airflow plenum between the one of the air inlet sides orthe air outlet sides of the at least two separate electronics racks andthe air-to-liquid heat exchanger of the multi-rack door.
 4. Theair-cooling apparatus of claim 3, wherein the structural extender has arectangular-shaped cross-section transverse to a direction of airflowthrough the at least two separate electronics racks, and is configuredto form an airtight seal with the at least two separate electronicsracks along upper, lower, and side edges thereof at the one of the airinlet sides or the air outlet sides of the at least two separateelectronics racks, and wherein the structural extender defining thecommon airflow plenum is configured to ensure that substantially all airpassing through the one of the air inlet sides or the air outlet sidesof the at least two separate electronics racks passes across theair-to-liquid heat exchanger.
 5. The air-cooling apparatus of claim 1,wherein the air-to-liquid heat exchanger is in spaced, opposing relationto the one of the air inlet sides or the air outlet sides of the atleast two separate electronics racks held by the securing mechanism infixed relation, and the air-to-liquid heat exchanger has a largersurface area than a surface area of the air inlet side or air outletside in spaced, opposing relation therewith of each of the at least twoseparate electronics racks.
 6. The air-cooling apparatus of claim 1,wherein the securing mechanism comprises a slidable engagement structuredisposed between the at least two separate electronics racks and holdingthe at least two separate electronics racks in fixed relation adjacentto each other, the slidable engagement structure allowing a firstelectronics rack of the at least two separate electronics racks to beslidably positioned adjacent to, and held in fixed relation to, a secondelectronics rack of the at least two separate electronics racks.
 7. Amulti-rack assembly comprising: a first electronics rack comprising atleast one heat-generating electronic component, the first electronicsrack comprising an air inlet side and an air outlet side respectivelyenabling ingress and egress of external air; a second electronics rackcomprising at least one heat-generating electronic component, the secondelectronics rack comprising an air inlet side and an air outlet siderespectively enabling ingress and egress of external air; an air-coolingapparatus for extracting heat from airflow passing through the firstelectronics rack and the second electronics rack, the apparatuscomprising: a securing mechanism for holding the first electronics rackand the second electronics rack in fixed relation adjacent to eachother, the securing mechanism holding the first electronics rack and thesecond electronics rack in fixed relation adjacent to each other withthe air inlet sides facing a first direction and the air outlet sidesfacing a second direction; and a multi-rack door sized and configured tospan one of the air inlet sides or the air outlet sides of the first andsecond electronics racks held by the securing mechanism in fixedrelation, the multi-rack door comprising: a door frame with an airflowopening, the airflow opening facilitating the ingress or egress ofairflow through the first and second electronics racks; and anair-to-liquid heat exchanger supported by the door frame and disposed sothat airflow through the airflow opening passes across the air-to-liquidheat exchanger, the air-to-liquid heat exchanger extracting heat fromthe airflow passing thereacross, and wherein air passing through the oneof the air inlet sides or the air outlet sides of the first and secondelectronics racks passes across the air-to-liquid heat exchanger;wherein the securing mechanism comprises an adapter frame sized andconfigured to mount to the first and second electronics racks at the oneof the air inlet sides or the air outlet sides thereof, and to hold thefirst and second electronics racks in fixed relation adjacent to eachother, and the adapter frame has a depth greater than a depth of themulti-rack door in a direction of airflow through the first and secondelectronics racks from the air inlet sides to the air outlet sidesthereof.
 8. The multi-rack assembly of claim 7, wherein the multi-rackdoor hingedly mounts to the adapter frame, and the adapter framecomprises a structural extender configured to mount to the first andsecond electronics racks at the one of the air inlet sides or the airoutlet sides thereof, and to facilitate defining a common airflow plenumbetween the one of the air inlet sides or the air outlet sides of thefirst and second electronics racks and the air-to-liquid heat exchangerof the multi-rack door.
 9. The multi-rack assembly of claim 8, whereinthe structural extender has a rectangular-shaped cross-sectiontransverse to a direction of airflow through the first and secondelectronics racks, and is configured to form an airtight seal with thefirst and second electronics racks along upper, lower, and side edgesthereof at the one of the air inlet sides or the air outlet sides of thefirst and second electronics racks, and wherein the structural extenderfacilitating defining the common airflow plenum is configured to ensurethat substantially all air passing through the one of the air inletsides or the air outlet sides of the first and second electronics rackspasses across the air-to-liquid heat exchanger.
 10. A method comprising:providing a securing mechanism for holding at least two separateelectronics racks in fixed relation adjacent to each other, the at leasttwo separate electronics racks being at least partially air-cooled, andeach having an air inlet side and an air outlet side, the securingmechanism holding the at least two separate electronics racks in fixedrelation adjacent to each other with the air inlet sides facing a firstdirection and the air outlet sides facing a second direction; andproviding a multi-rack door sized and configured to span one of the airinlet sides or the air outlet sides of the at least two separateelectronics racks held by the securing mechanism in fixed relation, themulti-rack door comprising: a door frame with an airflow opening, theairflow opening facilitating the ingress and egress of airflow throughthe at least two separate electronics racks; and an air-to-liquid heatexchanger supported by the door frame and disposed so that airflowthrough the airflow opening passes across the air-to-liquid heatexchanger, the air-to-liquid heat exchanger extracting heat from theairflow passing thereacross, and wherein air passing through the one ofthe air inlet sides or the air outlet sides of the at least two separateelectronics racks passes across the air-to-liquid heat exchanger; andwherein the securing mechanism comprises an adapter frame sized andconfigured to mount to the at least two separate electronics racks atthe one of the air inlet sides or the outlet sides thereof, and to holdthe at least two separate electronics racks in fixed relation adjacentto each other, and the adapter frame has a depth greater than a depthgreater than a depth of the multi-rack door in a direction of airflowthrough the at least two separate electronics racks from the air inletsides to the air outlet sides thereof.
 11. The method of claim 10,wherein the multi-rack door hingedly mounts to the adapter frame, andthe adapter frame comprises a structural extender configured to mount tothe at least two separate electronics racks at the one of the air inletsides or the air outlet sides thereof, and to facilitate defining acommon airflow plenum between the one of the air inlet sides or the airoutlet sides of the at least two separate electronics racks and theair-to-liquid heat exchanger of the multi-rack door.